It has generally been considered to provide auto-focus capabilities in a digital projector. Consistent with an auto-focus capability, the digital projector projects an image onto a projection screen, captures an image of the projected image, and moves the focus of the projection lens iteratively in order to move from an out-of-focus position toward an in-focus position.
Correction of focus is typically an iterative, multi-step process. In a first step, a first image is captured. The focus position of the lens is then moved in an arbitrary direction, such as a forward direction toward the screen. A second image is then captured. The focus condition of the first image is compared against the focus condition of the second image. If focus has improved, then the projection lens is iteratively moved in the same direction as before. On the other hand, if focus condition has not improved, then it is assumed that the projection lens had been moved in the wrong direction. Accordingly, the projection lens is moved in the reverse direction. These steps are repeated iteratively, until an adequate in-focus condition is achieved.
It has also been considered to provide projectors with distance-measuring equipment, and to adjust focus based on a measured distance between the projector and the projection screen. Such arrangements differ from the arrangements contemplated herein.